That's really easy to do, anywhere. Just fly towards them quickly and jump over their heads, hope they don't move, and then keep charging up and using your blast 2s. I do that all the time.
I got all my dragonballs at the city.
Personally, I don't like mountain road. It's too small. I like they hyperbolic time chamber cause it's really easy to find people, so it's pretty much a forced fight arena.